Motor drive circuit and electric compressor having the same

ABSTRACT

A motor drive circuit for driving an electric motor in an electric compressor has a substrate and a plurality of electrical components. The compressor includes a compressor housing having a circumferential wall around a central axis of the compressor. The circumferential wall has a substantially cylindrical surface. The substrate is arranged outside the circumferential wall and includes a first portion and a second portion. The first portion is closer to the central axis than the second portion. The electrical components are mounted on the substrate on the near side relative to the central axis and include short electrical components that have relatively short height from the substrate and tall electrical components that have relatively tall height from the substrate. The electrical components line the cylindrical surface of the circumferential wall in such a manner that the short and tall electrical components are respectively arranged at the first and second portions.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a motor drive circuit fordriving an electric motor in an electric compressor and to an electriccompressor with the motor drive circuit.

[0002] Unexamined Japanese Patent Publication No. 2002-155863 disclosesa conventional electric compressor. For example, referring to FIG. 5, adiagram illustrates a front end view of a motor compressor or anelectric compressor 100 according to a prior art. A compressor housing101 forms an outer shell of the motor compressor 100. An electric motor102 and a compression mechanism 103 are accommodated in the compressorhousing 101. The compressor housing 101 includes a cylindricalcircumferential wall 101 a around a central axis L of the motorcompressor 100, and a motor drive circuit 104 is arranged outside thecircumferential wall 101 a. The motor drive circuit 104 includes aninverter and the like for driving the electric motor 102. A casing seat105 has a planar fixing surface 105 a and is provided on thecircumferential wall 101 a of the compressor housing 101. A planarcasing 106 for accommodating the motor drive circuit 104 is joined tothe fixing surface 105 a of the casing seat 105.

[0003] An unwanted feature is that the motor drive circuit 104 largelyprotrudes in the transverse direction of the compressor housing 10because the cylindrical circumferential wall 101 a of the compressorhousing 101 is different in shape from the planar casing 106 of themotor drive circuit 104. Accordingly, the motor compressor 100 isrelatively large in size in the radial direction of the central axis L.

[0004] Additionally, the casing seat 105 needs to be provided on thecircumferential wall 101 a of the compressor housing 101 to compensatefor the difference in shape between the cylindrical circumferential wall101 a and the planar casing 106. Thus, the motor compressor 100 becomesheavy by the mass of the casing seat 105. Furthermore, for example, whenthe compressor housing 101 is manufactured integrally with the casingseat 105 by die-casting, some trouble such as a mold cavity is possiblyproduced at the thick portion of the casing seat 105. Therefore, thereis a need for a motor drive circuit and an electric compressor with themotor drive circuit that contribute to reducing the size and weight ofthe electric compressor.

SUMMARY OF THE INVENTION

[0005] In accordance with the present invention, a motor drive circuitfor driving an electric motor in an electric compressor has a substrateand a plurality of electrical components. The compressor includes acompressor housing having a circumferential wall around a central axisof the compressor. The circumferential wall has a substantiallycylindrical surface. The substrate is arranged outside thecircumferential wall and includes a first portion and a second portion.The first portion is closer to the central axis than the second portion.The electrical components are mounted on the substrate on the near siderelative to the central axis and include short electrical componentsthat have relatively short height from the substrate and tall electricalcomponents that have relatively tall height from the substrate. Theelectrical components line the cylindrical surface of thecircumferential wall in such a manner that the short and tall electricalcomponents are respectively arranged at the first and second portions.

[0006] Other aspects and advantages of the invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The features of the present invention that are believed to benovel are set forth with particularity in the appended claims. Theinvention together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

[0008]FIG. 1 is a longitudinal cross-sectional view of a motorcompressor according to a preferred embodiment of the present invention;

[0009]FIG. 2 is a side view of the motor compressor according to thepreferred embodiment of the present invention;

[0010]FIG. 3 is a partially enlarged cross-sectional view that is takenalong the line I-I in FIG. 2 in a state when an electric motor isdetached;

[0011]FIG. 4 is a partially enlarged cross-sectional view of a motorcompressor according to an alternative embodiment of the presentinvention; and

[0012]FIG. 5 is a front end view of a motor compressor according to aprior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A preferred embodiment of the present invention will now bedescribed in reference to FIGS. 1 through 3.

[0014] Now referring to FIG. 1, a diagram illustrates a longitudinalcross-sectional view of a motor compressor or an electric compressor 10according to the preferred embodiment of the present invention. Acompressor housing 11 forms an outer shell of the motor compressor 10and includes a first housing element 21 and a second housing element 22.The first housing element 21 has a substantially cylindricalcircumferential wall 23 and an end wall that is formed on the left endof the circumferential wall 23 in the drawing. The first housing element21 is die-cast in an aluminum alloy. The second housing element 22 formsa cylinder with an end wall on the right end in the drawing and isdie-cast in an aluminum alloy. The first and second housing elements 21,22 are fixedly connected with each other so that a closed space 24 isdefined in the compressor housing 11.

[0015] A rotary shaft 27 is rotatably supported by the first housingelement 21 in the closed space 24 and has a central axis of rotationthat is identical to the central axis L of the motor compressor 10. Thecircumferential wall 23 of the first housing element 21 surrounds thecentral axis L of the motor compressor 10.

[0016] An electric motor 25 and a compression mechanism 26 areaccommodated in the closed space 24. The electric motor 25 is abrushless direct current type or a brushless DC type and includes astator 25 a and a rotor 25 b. The stator 25 a is fixedly connected to aninner surface 23 a of the circumferential wall 23 of the first housingelement 21. The rotor 25 b is provided on the rotary shaft 27 and isarranged inside the stator 25 a. The electric motor 25 rotates therotary shaft by electric power that is supplied to the stator 25 a.

[0017] The compression mechanism 26 is a scroll type and includes afixed scroll member 26 a and a movable scroll member 26 b. As themovable scroll member 26 b orbits relative to the fixed scroll member 26a in accordance with the rotation of the rotary shaft 27, thecompression mechanism 26 compresses refrigerant gas or fluid. An outlet32 is formed in the second housing element 22 for discharging thecompressed refrigerant gas to an external refrigerant circuit, which isnot shown in the drawing.

[0018] As the electric motor 25 drives the compression mechanism 26, therefrigerant gas in relatively low temperature and relatively lowpressure is introduced from the external refrigerant circuit into thecompression mechanism 26 through the electric motor 25. The introducedrefrigerant gas is compressed to have relatively high temperature andrelatively high pressure by the compression mechanism 26. Then, therefrigerant gas is discharged to the external refrigerant circuitthrough the outlet 32. Incidentally, the refrigerant gas in relativelylow temperature from the external refrigerant circuit cools the electricmotor 25 as it passes by the electric motor 25.

[0019] Now referring to FIG. 2, a diagram illustrates a side view of themotor compressor 10 according to the preferred embodiment of the presentinvention. An inlet 31 is formed in the first housing element 21. Therefrigerant gas is introduced from the external refrigerant circuit intothe compressor housing 11 through the inlet 31.

[0020] Now referring to FIG. 3, a diagram illustrates a partiallyenlarged cross-sectional view that is taken along the line I-I in FIG.2. An outer surface 23 b of the circumferential wall 23 is mostly formedalong a cylindrical surface R having the central axis L. The firsthousing element 21 partially includes an accommodating portion 36. Theaccommodating portion 36 is provided on a portion of the outer surface23 b of the circumferential wall 23 and defines an accommodating space35 inside. The accommodating portion 36 includes a frame-shaped sidewall 37 and a cover member 38. The side wall 37 is integrally formedwith the circumferential wall 23 and extends from the outer surface 23b. The cover member 38 is fixedly connected to the distal end surface ofthe side wall 37 by a fixing frame 40. The cover member 38 forms a thinplate and is made of metal such as an aluminum alloy. A seal member 39is interposed between the distal end surface of the side wall 37 and theouter peripheral portion of the cover member 38 for sealing theaccommodating space 35.

[0021] The outer surface 23 b of the circumferential wall 23 defines abottom surface 35 a of the accommodating space 35. In other words, thebottom surface 35 a is formed on the left end of the accommodating space35 in the drawing. The inner surface of the side wall 37 defines a sidesurface 35 b of the accommodating space 35. Namely, the first housingelement 21 defines the bottom and side surfaces 35 a, 35 b of theaccommodating space 35. The cover member 38 defines a top surface 35 cof the accommodating space 35. In other words, the top surface 35 c isformed on the right end of the accommodating space 35 in the drawing.

[0022] A motor drive circuit 41 is accommodated in the accommodatingspace 35 in the accommodating portion 36 for driving the electric motor25. The motor drive circuit 41 includes an inverter and supplies thestator 25 a of the electric motor 25 with electric power based on acommand from an air conditioner ECU, which is not shown in the drawing.Incidentally, the refrigerant gas cools the motor drive circuit 41 as itis introduced from the external refrigerant circuit to the compressionmechanism 26 through the electric motor 25.

[0023] The motor drive circuit 41 includes a planar substrate 43 and aplurality of electrical components 44. The substrate 43 is fixedlyconnected to the circumferential wall 23 by a fastener, such as a bolt,which is not shown in the drawing. The substrate 43 is substantially inparallel with the central axis L of the motor compressor 10. Theelectrical components 44 are respectively mounted on surfaces 43 a, 43 bof the substrate 43. Namely, the electrical components 44 arerespectively mounted on the substrate 43 on the near and far sidesrelative to the central axis L. Incidentally, the electrical components44 include electrical components 44A through 44E and other electricalcomponents, which are not shown in the drawing.

[0024] The electrical components 44 include known components forconstituting the inverter. That is, the electrical components 44 includea switching device 44A, an electrolytic condenser 44B, a transformer44C, a driver 44D, a fixed resistance 44E and the like. The driver 44Dis an integrated circuit chip or an IC chip for intermittentlycontrolling the switching device 44A based on a command from the airconditioner ECU.

[0025] The switching device 44A has a height of h3 from the substrate 43and is mounted on the surface 43 a of the substrate 43, that is, on thesubstrate 43 on the near side relative to the central axis L. Some ofthe electrical components 44 are shorter than the switching device 44Aif they are mounted on the same surface. The shorter electricalcomponents 44 correspond to second electrical components. Only the aboveshorter electrical components 44 are mounted on the surface 43 b of thesubstrate 43, that is, on the substrate 43 on the far side relative tothe central axis L. The above shorter electrical components 44 includethe driver 44D and the fixed resistance 44E.

[0026] Some of the electrical components 44 have heights of h1, h2 fromthe substrate 43 and are taller than the switching device 44A. Thetaller electrical components 44 and the switching device 44A are mountedon the surface 43 a of the substrate 43, that is, on the substrate 43 onthe near side relative to the central axis L. The taller electricalcomponents 44 correspond to first electrical components. The tallerelectrical components 44 include the electrolytic condenser 44B and thetransformer 44C. Accordingly, among the electrical components 44 on thesurface 43 a of the substrate 43, the switching device 44A correspondsto a short electrical component that has a relatively short height of h3from the substrate 43, and the electrolytic condenser 44B and thetransformer 44C correspond to tall electrical components that haverelatively tall heights of h1, h2.

[0027] In the preferred embodiment, the electrical components 44 on thesurface 43 a are arranged as follows. The short electrical componentssuch as the switching device 44A are arranged at the middle portion ofthe surface 43 a of the substrate 43. The middle portion of the surface43 a of the substrate 43 corresponds to a first portion thereof. Thetall electrical components such as the electrolytic condenser 44B andthe transformer 44C are arranged at both ends of the surface 43 a, thatis, the upper and lower ends of the surface 43 a in FIG. 3. The upperand lower ends of the surface 43 a of the substrate 43 correspond to asecond portion thereof. Namely, the short electrical components arearranged relatively closer to the central axis L, while the tallelectrical components are arranged relatively farther from the centralaxis L. As arranged above, the motor drive circuit 41 is installed tothe compressor housing 11 in such a manner that the electricalcomponents 44 on the surface 43 a of the substrate 43 line thecylindrical surface R of the circumferential wall 23. Incidentally, theswitching device 44A, the electrolytic condenser 44B and the transformer44C each are plurally arranged in the direction of the central axis L.

[0028] A clearance between the bottom surface 35 a and the top surface35 c is relatively narrow at the middle region of the accommodatingspace 35 in the accommodating portion 36, and the short electricalcomponents such as the switching device 44A are arranged at the middleregion of the accommodating space 35. Clearances between the bottomsurface 35 a and the top surface 35 c are relatively wide at both endregions relative to the middle region of the accommodating space 35, andthe tall electrical components such as the electrolytic condenser 44Band the transformer 44C are arranged at the above end regions. Namely,the bottom surface 35 a of the accommodating space 35 includes a convexsurface at its middle where the bottom surface 35 a approaches the topsurface 35 c to the maximum. Accordingly, in comparison to anaccommodating space that includes an entire planar bottom surface, theaccommodating space 35 partially forms the shape along the cylindricalsurface R of the circumferential wall 23.

[0029] In the motor drive circuit 41 in the accommodating space 35, theelectrical components 44 are arranged on the surface 43 a of thesubstrate 43 along the cylindrical surface R of the circumferential wall23. Therefore, the motor drive circuit 41 is arranged to approach thecentral axis L of the motor compressor 10 because the electricalcomponents 44 line the cylindrical surface R of the circumferential wall23.

[0030] The substrate 43 is arranged at a distance of h4 from thecylindrical surface R. The distance h4 is shorter than the height h1 ofthe electrolytic condenser 44B that is the tallest in the electricalcomponents 44. The cylindrical surface R of the circumferential wall 23approaches the surface 43 a of the substrate 43 without any interferencewith the electrical components 44 on the surface 43 a, that is, withoutcrossing the electrical components 44 on the surface 43 a. Namely, themotor drive circuit 41 is arranged near the central axis L of the motorcompressor 10 so that the cylindrical surface R of the circumferentialwall 23 is arranged at the distance h4 from the substrate 43 and thedistance h4 is shorter than the height h1 of the electrolytic condenser44B.

[0031] In the preferred embodiment, “the electrical components 44 linethe cylindrical surface R of the circumferential wall 23” means a statewhere the the cylindrical surface R of the circumferential wall 23approaches the surface 43 a in such a manner that the distance h4 fromthe substrate 43 at least becomes shorter than the height h1 of theelectrolytic condenser 44B while the cylindrical surface R of thecircumferential wall 23 does not interfere with the electricalcomponents 44 on the surface 43 a.

[0032] Particularly, in the preferred embodiment, the cylindricalsurface R of the circumferential wall 23 approaches the surface 43 a ofthe substrate 43 in such a manner that the distance h4 from thesubstrate 43 becomes shorter than the height h2 of the transformer 44C,which is the second tallest, and the cylindrical surface R does notinterfere with the electrical components 44 on the surface 43 a.Accordingly, the electrical components 44 on the surface 43 a adjacentlyline the cylindrical surface R of the circumferential wall 23 so thatthe motor drive circuit 41 is arranged near the central axis L muchcloser.

[0033] In the motor drive circuit 41, the switching device 44A, theelectrolytic condenser 44B and the transformer 44C are in contact withthe bottom surface 35 a of the accommodating space 35 through a sheet oran insulating member 45 made of rubber or resin. Namely, the sheet 45 isinterposed between the electrical components 44A, 44B, 44C and the firsthousing element 21 made of aluminum, respectively. A material havingproperties of relatively high elasticity and/or relatively high heatconductivity is employed as the sheet 45. A clearance between the topsurface 35 c of the cover member 38 and the motor drive circuit 41 isfilled with a filler or an insulating member 46 made of rubber or resin.The filler 46 has properties of relatively high elasticity and/orrelatively high heat conductivity.

[0034] According to the preferred embodiment, the following advantageouseffects are obtained.

[0035] (1) The short electrical components, such as the switching device44A, are mounted on the surface 43 a on the near side relative to thecentral axis L of the motor compressor 10 and are arranged closer to thecentral axis L. In addition, the tall electrical components, such as theelectrolytic condenser 44B and the transformer 44C, are arranged on thesurface 43 a of the substrate 43 and are arranged farther from thecentral axis L. This arrangement allows the electrical components 44 onthe surface 43 a to line the cylindrical surface R of thecircumferential surface 23. The accommodating portion 36 on thecompressor housing 11 defines the accommodating space 35 foraccommodating the motor drive circuit 41 in such a manner that theaccommodating space 35 is formed along the cylindrical surface R of thecircumferential wall 23.

[0036] Accordingly, in the motor drive circuit 41 accommodated in theaccommodating space 35, the electrical components 44 on the surface 43 aof the substrate 43 line the cylindrical surface R of thecircumferential wall 23. Since the electrical components 44 line thecylindrical surface R, the motor drive circuit 41 is arranged relativelyclose to the central axis L of the compressor housing 11. Thus, theprotrusion of the motor drive circuit 41 from the compressor housing 11in the direction perpendicular to the central axis L is controlled at arelatively small amount so that the motor compressor 10 becomes small indiameter.

[0037] Furthermore, the motor drive circuit 41 is arranged close to thecentral axis L of the motor compressor 10, which means that a wall or amaterial, such as the casing seat 105 shown in FIG. 5, is reduced inthickness between the motor drive circuit 41 and the compressor housing11. Accordingly, the motor compressor 10 becomes light in weight andbecomes low-cost due to the reduction in the material. Furthermore, sometrouble, such as a mold cavity, does not substantially occur in thedie-cast compressor housing 11 due to the reduction in the material.

[0038] (2) On the surface 43 a of the substrate 43, the short electricalcomponents such as the switching device 44A are arranged at the middleportion, and the tall electrical components such as the electrolyticcondenser 44B and the transformer 44C are respectively arranged on bothsides to the middle portion. Thus, the tall electrical components aredistributed on both sides to the short electrical components so thatmany of the electrical components 44 line the circumferential directionof the circumferential wall 23. Accordingly, the substrate 43 isprevented from enlarging in size in the direction of the central axis L.That is, the motor compressor 10 is prevented from enlarging in size inthe direction of the central axis L, while it is effectively reduced insize.

[0039] (3) In the accommodating portion 36, the compressor housing 11defines the bottom and side surfaces 35 a, 35 b of the accommodatingspace 35. Accordingly, in comparison to an accommodating portion that isindependent to the compressor housing 11, for example, the casing 106illustrated in FIG. 5, the number of components is reduced in the motorcompressor 10. Additionally, the compressor housing 11 having relativelyhigh rigidity surrounds the motor drive circuit 41 and effectivelyprotects the motor drive circuit 41 against an impact from the outside.

[0040] (4) On the substrate 43 on the near side relative to the centralaxis L, the electrical components 44A through 44C are in contact withthe bottom surface 35 a of the accommodating space 35 through theinsulative sheet 45. In comparison to a state when an insulating spaceor a relatively large space is defined between the electrical components44A through 44C and the bottom surface 35 a of the accommodating space35, the motor drive circuit 41 is arranged closer to the central axis Lin the preferred embodiment. Accordingly, the motor compressor 10 isfurther reduced in size and weight. Additionally, in comparison to astate when an insulating space is defined, heat generated from theelectrical components 44A through 44C is efficiently conducted to thecompressor housing 11 so that the motor drive circuit 41 is efficientlycooled.

[0041] Furthermore, when the sheet 45 employs a material havingrelatively high heat conductivity, it contributes to further efficientlycooling the motor drive circuit 41. Meanwhile, when the sheet 45 employsa material having relatively high elasticity, it contributes toprotecting the motor drive circuit 41 against an impact from theoutside. In addition, the sheet 45 elastically deforms to cancel adimensional tolerance so that the electrical components 44A through 44Care in firmly contact with the bottom surface 35 a of the accommodatingspace 35. This leads to improvement in heat radiation performance of theelectrical components 44A through 44C to the compressor housing 11.

[0042] (5) The metal cover member 38 is fastened to the compressorhousing 11 for defining the top surface 35 c of the accommodating space35. The insulative filler 46 is interposed between the top surface 35 cand the motor drive circuit 41. The combination of the metal covermember 38 and the metal compressor housing 11 surrounds the motor drivecircuit 41. Accordingly, electromagnetic wave generated by the motordrive circuit 41 is prevented from leaking outside for efficientlysuppressing noise toward the other electrical components.

[0043] Furthermore, in comparison to an insulating space or a largespace is defined between the motor drive circuit 41 and the top surface35 c of the accommodating space 35, the filler 46 is interposed betweenthe motor drive circuit 41 and the top surface 35 c of the accommodatingspace 35 so that the top surface 35 c is arranged relatively close tothe central axis L, that is, the cover member 38 is arranged relativelyclose to the central axis L. Accordingly, the motor compressor 10 isfurther reduced in size. Also, in comparison to a state when aninsulating space is defined, heat generated by the motor drive circuit41 is efficiently conducted through the cover member 38 so that themotor drive circuit 41 is efficiently cooled.

[0044] When the filler 46 employs a material having relatively high heatconductivity, it contributes to further efficiently cooling the motordrive circuit 41. Meanwhile, since the filler 46 employs a materialhaving relatively high elasticity, it contributes to protecting themotor drive circuit 41 against an impact from the outside. In addition,the filler 46 elastically deforms to cancel a dimensional tolerance sothat the motor drive circuit 41 is in firmly contact with the covermember 38. This leads to improvement in heat radiation performance ofthe motor drive circuit 41 to the cover member 38.

[0045] The present invention is not limited to the embodiments describedabove but may be modified into the following alternative embodiments.

[0046] In alternative embodiments to the above preferred embodiment,referring to FIG. 4, a diagram illustrates a partially enlargedcross-sectional view of a motor compressor. When the motor compressorhas a relatively large space in the direction of the central axis L formounting the electrical components 44, the tall electrical componentssuch as the electrolytic condenser 44B is arranged on one side to theshort electrical components such as the switching device 44A in themotor drive circuit 41. Additionally, the transformer 44C is not shownin the drawing. However, the transformer 44C is arranged on the surface43 a on the far side relative to the central axis L in such a mannerthat the electrolytic condenser 44B and the transformer 44C line in thedirection of the central axis L.

[0047] In alternative embodiments to the above preferred embodiment, anelectric motor and a compression mechanism are respectively accommodatedin different compressor housings in a motor compressor. In this state, amotor drive circuit is arranged in one of the compressor housing thataccommodates the electric motor and the other that accommodates thecompression mechanism.

[0048] In alternative embodiments to the above preferred embodiment, themotor compressor is a hybrid compressor that includes two drive sourcesfor driving the compression mechanism 26. The two drive sources are anelectric motor and an engine for driving a vehicle.

[0049] In alternative embodiments to the above preferred embodiment, thecompression mechanism 26 is not limited to a scroll type. For example, apiston type, a vane type and a helical type are applicable.

[0050] Therefore, the present examples and embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein but may be modified within thescope of the appended claims.

What is claimed is:
 1. A motor drive circuit for driving an electricmotor in an electric compressor, the compressor including a compressorhousing that has a circumferential wall around a central axis of thecompressor, the circumferential wall having a substantially cylindricalsurface, the motor drive circuit comprising: a substrate arrangedoutside the circumferential wall, the substrate including a firstportion and a second portion, the first portion being closer to thecentral axis than the second portion; and a plurality of firstelectrical components mounted on the substrate on the near side relativeto the central axis, the first electrical components including shortelectrical components that have relatively short height from thesubstrate and tall electrical components that have relatively tallheight from the substrate, wherein the first electrical components linethe cylindrical surface of the circumferential wall in such a mannerthat the short and tall electrical components are respectively arrangedat the first and second portions.
 2. The motor drive circuit accordingto claim 1, wherein the first portion is a middle portion of thesubstrate, the substrate leaving away from the central axis as thesubstrate extends from the middle portion toward both sides relative tothe middle portion, the tall electrical components being arranged onboth sides relative to the middle portion.
 3. The motor drive circuitaccording to claim 1, wherein the substrate forms a planar in shape. 4.The motor drive circuit according to claim 3, wherein the substrate issubstantially in parallel with the central axis.
 5. The motor drivecircuit according to claim 1, wherein the substrate leaves away from thecentral axis as the substrate extends from the first portion toward oneside relative to the first portion, the tall electrical components beingarranged on the one side relative to the first portion.
 6. The motordrive circuit according to claim 1, wherein the substrate is arranged ata predetermined distance from the cylindrical surface of thecircumferential wall, the predetermined distance being shorter than theheight of the tall electrical components.
 7. The motor drive circuitaccording to claim 1, wherein the tall electrical components include atleast one of an electrolytic condenser and a transformer.
 8. The motordrive circuit according to claim 1, wherein the short electricalcomponents include a switching device.
 9. The motor drive circuitaccording to claim 1, further comprising: a second electrical componentmounted on the substrate on the far side relative to the central axis,the second electrical component having shorter height than the shortelectrical components.
 10. The motor drive circuit according to claim 9,wherein the second electrical component includes at least one of adriver and a fixed resistance.
 11. An electric compressor comprising: acompressor housing having a circumferential wall around a central axisof the compressor and partially including an accommodating portion thatdefines an accommodating space along the cylindrical surface, thecircumferential wall having a substantially cylindrical surface; acompression mechanism arranged in the compressor housing for compressingfluid; an electric motor arranged in the compressor housing for drivingthe compression mechanism; and a motor drive circuit arranged in theaccommodating space for driving the electric motor, the motor drivecircuit including: a substrate arranged outside the circumferentialwall, the substrate including a first portion and a second portion, thefirst portion being closer to the central axis than the second portion;and a plurality of electrical components mounted on the substrate on thenear side relative to the central axis, the electrical componentsincluding short electrical components having relatively short heightfrom the substrate and tall electrical components having relatively tallheight from the substrate, wherein the electrical components line thecylindrical surface of the circumferential wall in such a manner thatthe short and tall electrical components are respectively arranged atthe first and second portions.
 12. The electric compressor according toclaim 11, wherein the compressor housing defines bottom and sidesurfaces of the accommodating space.
 13. The electric compressoraccording to claim 12, further comprising: a first insulating memberinterposed between the electrical components and the bottom surface ofthe accommodating space.
 14. The electric compressor according to claim13, wherein the first insulating member is made of material that isselected from the group consisting of rubber and resin.
 15. The electriccompressor according to claim 14, wherein the first insulating memberhas a property of at least one of relatively high elasticity andrelatively high heat conductivity.
 16. The electric compressor accordingto claim 12, further comprising: a metal cover member fastened to thecompressor housing for defining a top surface of the accommodatingspace; and a second insulating member interposed between the top surfaceand the motor drive circuit.
 17. The electric compressor according toclaim 16, wherein the second insulating member is made of material thatis selected from the group consisting of rubber and resin.
 18. Theelectric compressor according to claim 17, wherein the second insulatingmember has a property of at least one of relatively high elasticity andrelatively high heat conductivity.
 19. The electric compressor accordingto claim 11, wherein the substrate is arranged at a predetermineddistance from the cylindrical surface of the circumferential wall, thepredetermined distance being shorter than the height of the tallelectrical components.
 20. The electric compressor according to claim11, wherein the compression mechanism is a scroll type.